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10.1.0.0 network for Customer X and propagated that to P2. When a packet arrives at PE2, the router sees the VPN label first. Since PE2 assigned the label, it knows exactly where the packet goes.

F I G U R E 5 . 5 Forwarding packets without labels on VPNs with overlapping network addresses

Customer X 10.1.0.0/16

Customer Y 10.1.0.0/16

F I G U R E 5 . 6 Forwarding packets with labels on VPNs with overlapping network addresses

MP-BGP Configuration

MP-BGP must be configured between all routers that need to propagate or exchange VPN routes.

VPN routes are referred to as VPN version 4 (VPNv4) routes.

166 Chapter 5 MPLS VPNs

To configure MP-BGP, the address-family vpnv4 command is used from within the traditional BGP configuration. An address family is sometimes referred to as a routing context. In this case, the address family vpnv4 command is used within global BGP configuration. Therefore, this special context does not need a new BGP process. (Only one BGP is supported on a Cisco IOS router.) Neighbors, if already configured in global BGP, simply need to be activated.

Communities must be configured as well. There are two types of communities: extended and standard. Standard communities have not been replaced by extended communities. It is necessary to specify extended communities between MP-BGP neighbors for proper VPN operation. The default operation of BGP is to send no community values. Therefore, you must manually configure MP-BGP to send both standard and extended communities.

Based on the configuration illustrated in Figure 5.1 earlier in this chapter, the final task is to configure MP-BGP between PE1 and PE2. Just to refresh your memory, Figure 5.7 illustrates the example service provider network.

F I G U R E 5 . 7 A service provider network

PE1 P1 P2 PE2

Table 5.2 lists the IP addresses and interfaces for all the devices in the service provider network in Figure 5.7.

T A B L E 5 . 2 Service Provider IP Addressing

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On the PE1 router, you configure MP-BGP with the following commands:

PE1#config t

PE1(config)#router bgp 1 PE1(config-router)#address-family vpnv4

PE1(config-router)#neighbor 192.168.1.4 activate PE1(config-router)#neighbor 192.168.1.4 next-hop self PE1(config-router)#neighbor 192.168.1.4 send-community both

On the PE2 router, you configure MP-BGP with the following commands:

PE2#config t

PE2(config)#router bgp 1 PE2(config-router)#address-family vpnv4

PE2(config-router)#neighbor 192.168.1.1 activate PE2(config-router)#neighbor 192.168.1.1 next-hop self PE1(config-router)#neighbor 192.168.1.1 send-community both

A sample output from the show running-config command is as follows. In this output, locate the global BGP commands and then the MP-BGP commands under the address-family vpnv4 section:

router bgp 1

no synchronization

network 192.168.1.1 mask 255.255.255.255 neighbor 192.168.1.4 remote-as 1

neighbor 192.168.1.4 update-source Loopback0 redistribute static

!

address-family vpnv4

neighbor 192.168.1.4 activate neighbor 192.168.1.4 next-hop self

neighbor 192.168.1.4 send-community both

Neighbors are first specified in global BGP, and then for MP-BGP, neighbors

are activated.